Saturday 11 November 2000 21.09 EST
First published on Saturday 11 November 2000 21.09 EST

William BlakeTate Britain, London SW1 until 11 February

William Blake has been seen - in our time, if not his - as the patron saint of outsiders: an idealist working in complete defiance of establishment tastes who would rather cut off his hand than accept tainted money. He is born in Soho, refuses to go to church or school and never leaves the inner city except for a single trip during which he is charged with sedition.

An autodidact, trained only as a hack engraver, he develops the most original fusion of word and image in the history of art. Yet nobody comes to his first and last show - at the age of 53 - and his reputation is mainly for madness. Critics deride him as a lunatic, libertarian and nudist. Even fans like Wordsworth pity his afflicted visions, launching the myth of the Cockney nutcase.

The visions, of course, are amazing. Saints diving through the firmament, devils skating on water, angels backcrawling through seas of gossamer cloud. Blake imagined insects reincarnated as titans, tulips making love, Newton doing his maths at the bottom of the ink-blue ocean.

In his cosmos, the Queen of Heaven might hold an admiring mirror to her face and God might turn out a tyrant, wrenching Adam like a weed from the earth. To say that Blake turned the world upside down is no more than an understatement. That he persisted for more than 50 years, with no bosses and very few patrons, buried at 69 in an unknown grave: this is the crux of his heroism.

Tate Britain does not attempt to dislodge this popular image. How could it? With over 500 works, its Blake show is the largest ever mounted and the biggest event ever held at the Tate.

The sheer scale of Blake's reputation will make it almost impossible to get up close to the paintings - often no bigger than playing cards - and the punishing £8 entry fee means that most people won't be able to go twice. But these paper dreams are so fragile that there may never be another chance to see Blake at full stretch - and to see him anew as an artist.

Everything familiar is here: God in his chariot of fire, the Ancient of Days with his compasses, the Tyger, Newton, Jerusalem, the Songs of Innocence and Experience. There are the streaming bodies - words made flesh - the long hair, loose robes, rainbows and stars that made Blake such a hit with the hippies. But right away things start to look a little different. It's not just that Newton turns out to be fully as large as the Athena poster he became in the Seventies; nor that the Tyger, beneath Blake's burning words, is the size of a postage stamp. Two items in the very first room should scupper for good the cliché of Blake as a sky-gazing dreamer forever tripping over the curb.

The first is a tiny engraving from 1820, made around the time of his disastrous show. It's a drawing of an ancient sculpture: Laocoon and his sons tangled in a knot of serpents. Blake has tendentiously renamed the figures Jehovah, Adam and Satan. More than that, he has imprisoned them in a dense graffiti of slogans - 'Christianity is art: money its curse', 'Science is the tree of death' and so forth.

It's a full-scale rant, put there to remind you that Blake could be a denunciatory scourge. The text seems religious, but is planted with anti-enlightenment gibes against Newton and Locke, sly stabs at Joshua Reynolds, president of the RA, whose death Blake applauded in gleeful verse. Proud, sardonic, spiky, Blake held record grudges and regarded himself as the equal of Raphael and Dürer. Look at his illustrations to The Divine Comedy and you see Dante reproved, time and again.

The figures in those great watercolours are dressed appropriately in medieval robes, but the same garb looks shockingly anachro nistic when Blake is imagining revolutionary America or France. That's why the other object in that first room - a replica of Queen Eleanor's tomb in Westminster Abbey - is crucial. Blake made it the origin of his faux-Gothic figures with their hieratic faces, super-long bodies and drapes. He is a radical antiquarian, ransacking the past for the spirit of a better future. Skip a century and you see the same ambition in the Statue of Liberty.

Liberty, with her spiked diadem and triumphant arms, would be the woman for Blake if she wasn't so massy. His bodies are lithe, liable to levitate or fly. To see so many together is to realise just how far Blake departs from reality: prehensile toes, supernatural limbs, fingers that touch distant planets. Shape-shifters who can look like wraiths, sky-divers, even Spiderman, their every tendon is revealed beneath transparent robes and skin. The look is strenuous, never Romantically effete; yet each figure is airy, a figment of outline and wash that lives in the page.

Blake pioneered a printing technique - relief etching, in which everything but his images and words (written backwards) was corroded from the plate. Even this was a dig at Locke, whose concept of the mind as a tabula rasa waiting to be inscribed like a conventional engraving, disgusted Blake, who believed in innate ideas. The texts are handwritten, the images hand-touched so that they look more like watercolours. Blake freed his art from the tyranny of printers and typeface.

No matter where they're set - 1,000 leagues beneath the sea or outer space - his scenes are all choreographed in terms of the illuminated page. The figures merge with the words, sometimes passing over them in fireballs or spiral gusts. Pose is personality. Apollo performs an arabesque, Satan an Egyptian schmooze; Death takes a bow, arms imperiously outstretched. Blake can be corny: David delivered from the waves is like some Cecil B. DeMille finale. He can also be comic, tipping the damned into a tank of winking fish.

But you always know what's happening in these extreme, dynamic ballets. Or do you? Take Newton. Does anyone now interpret this superb figure, hunched over his sums, as a massive attack on Sir Isaac and all his works? Or recognise the Ancient of Days, with his wind-blown beard and lightning dividers, as Urizen, Blake's satirical personification of Reason? The later poems, with their druidical, Swedenborgian, occultist mythology, are as incomprehensible now as they probably ever were.

Tate Britain's attempts at interpretation are brave, but futile. Blake wasn't interested anyway: 'That which can be made explicit to the idiot is not worth my care.' The more obscure his texts, as this marvellous show reveals, the stronger the images - Urizen adrift, his beard floating across the waters; Albion rising in a blaze of glory; Jerusalem and Albion conceived as lovers, their twined embrace one of the supreme images of sexual love in art. 'The eye,' as Blake said, 'sees more than the heart knows.'

Apart from the occasional Regency curl and sideburn, these figures are timeless, their context eternal. To see them is to be taken out of yourself, removed to a fearless, liberated world.

If Blake was no more than official stenographer to the saints, as he mischievously claimed, then his best self-portrait is the late Recording Angel, pen in hand and seated, visions sparking above his head in a halo of stars.

What to focus on if you've only got an hour to spare

Nebuchadnezzar (1795) King Nebuchadnezzar, architect of Babylon, is a warning to the proud: 'those that walk in pride, the Lord can abase.' Blake's king crawls like a beast on the earth, beard trailing, toes turning to talons, naked skin like matted hide.

Newton (1805) Newton, a naked muscleman bent over his diagram, is so deeply absorbed that he doesn't notice the wonders of the coral-reefed ocean in which he is plunged. One of the 12 so-called large prints.

The Ghost of a Flea (1819) The flea is reincarnated as a creepy titan, holding the bowl in which he collects blood. Supposedly a vision transcribed for Blake's friend, the astrologer John Varley; possibly a tease at the credulous Varley.

The Tyger (1794) The poem from Songs of Innocence and Experience, famous as Wordsworth's 'Daffodils', with the big cat painted in fearful miniature below: religion, revolution and animal grandeur.

Jerusalem (1821) Not the national football anthem, later given that title, but the long poem in 100 magnificent plates. See especially the last, in which Jerusalem and Albion are united in erotic love within the petals of a lily.

Oh! Flames of Furious Desires (1796) From the First Book of Urizen, one of Blake's made-up mythologies. Incredibly tensile drawing of a figure leaping like Nijinsky through a veil of fire. Bear in mind Blake's belief that 'All is not sinful that Satan calls so'.

Capaneus the Blasphemer (1824) From Blake's illustrations to Dante's Divine Comedy. Capaneus, nude but still coiffed like a Regency dandy, reclines in the third circle of hell. His face is lit from beneath by flames, lightning strikes at his molten body.

The Ancient of Days (1824) The divine, reaching down from his burning disc, to measure the earth below with his lightning-bright dividers. Despite the force, and the white, windswept beard, this is not God but Blake's Urizen, the despised personification of Reason and Science.